1. Field of the Invention
The present invention relates to a polymer scale preventive agent in polymerization of a monomer having an ethylenically unsaturated double bond, a polymerization vessel effective in preventing polymer scale deposition, and a process of producing polymer using said vessel.
2. Description of the Prior Art
In processes of preparing polymers by polymerizing a monomer in a polymerization vessel, the problem that polymer deposits on the inner wall surface and so forth in the form of scale, is known. The deposition of the polymer scale on the inner wall results in disadvantages that the yield of the polymer and cooling capacity of the polymerization vessel are lowered; that the polymer scale may peel and mix into manufactured polymer, thereby impairing the quality thereof; and that removal of such polymer scale is laborious and hence time-consuming. Further, since the polymer scale contains unreacted monomer, operators may be exposed thereto, which may cause physical disorders in the operators.
Heretofore, as methods for preventing polymer scale deposition on the inner wall surface and so forth of a polymerization vessel in polymerization of a monomer having an ethylenically unsaturated double bond, methods in which substances exemplified below are coated on the inner wall surface, etc. as a scale preventive agent, hate been known.
For example, particular polar organic compounds (Japanese Patent Publication (KOKOKU) No. 45-30343(1970)), a dye or pigment (Japanese Patent Publication (KOKOKU) Nos. 45-30835(1970) and 52-24953(1977)), an aromatic amine compound (Japanese Pre-examination Patent Publication (KOKAI) No. 51-50887(1976)), a reaction product of a phenolic compound and an aromatic aldehyde (Japanese Pre-examination Patent Publication (KOKAI) No. 55-54317(1980)) and an electron-donating compound and/or an electron-accepting compound (Japanese Patent Publication (KOKOKU) No. 53-46235(1978) are disclosed.
According to the methods using these substances, one operation of forming a coating on the inner wall of a polymerization vessel enables repetition of polymerization runs without formation of scale deposition on the area of the liquid phase inside the polymerization vessel.
However, since scale deposition is generally liable to occur in the vicinity of the interface between the gas phase and liquid phase, which is located at an upper section in a polymerization vessel, scale deposition may take place on this area if a coating of a conventional polymer scale preventive agent mentioned above is formed. Once scale is deposited in the vicinity of the interface between the gas and liquid phases, the deposited scale will grow as polymerization runs are repeated, causing increase in fish eyes, one of the properties to be reduced from viewpoint of quality, of formed products.
That is, if polymer scale depositing on the vicinity of the interface between the gas and liquid phases has grown, it may be peeled and incorporated into a polymeric product. When the polymeric product containing the peeled scale is processed into formed products such as sheets or the like, the peeled scale causes many fish eyes in the formed products, lowering the quality thereof seriously.